26 HOW TO TREAT : IS THIS LYME DISEASE ?
26 HOW TO TREAT : IS THIS LYME DISEASE ?
15 SEPTEMBER 2023 ausdoc . com . au
PAGE 24 removal for species identification is useful for risk assessment ; however , molecular testing to identify if the tick is infected with B . burgdorferi sl is not recommended . 18 A bite from an Ixodes sp . tick increases the risk of Lyme disease , but the presence of B . burgdorferi sl in the tick does not reliably predict transmission or clinical infection and should not change management in an asymptomatic person .
In patients with skin lesions atypical for erythema migrans or with suspected disseminated or late Lyme disease , serological testing is needed to achieve a diagnosis . Testing for B . burgdorferi sl antibodies on acute and convalescent serum , 4-8 weeks apart , is recommended , to demonstrate the development of B . burgdorferi sl antibodies or a fourfold rise in B . burgdorferi sl IgG antibodies .
Occasionally , in specific cases , molecular testing may be useful . The Royal College of Pathologists of Australasia ( RCPA ) position statement on diagnostic laboratory testing for Lyme disease recommends that a biopsy of the rash in early acute Lyme is probably the best specimen . Other specimens — including synovial fluid and CSF — could be considered , but because Lyme disease has such low levels of spirochaetemia , blood PCR is of no value . As it can be difficult to obtain appropriate samples from patients , the RCPA considers this type of testing to be valuable for clinical research but of limited clinical utility at present . 6
Specialist referral is warranted if there is severe disease or end-organ complications due to suspected Lyme disease . In neuroborreliosis involving the peripheral or CNS , diagnosis should be made in the appropriate clinical context using serological testing to show the development of B . burgdorferi sl antibodies . Pair CSF analysis with a serum specimen to measure the CSF : serum antibody index and demonstrate B . burgdorferi – specific antibody production in the CSF . In Lyme arthritis , in addition to serum antibody testing , consider PCR testing for B . burgdorferi sl in synovial fluid or tissue in seropositive patients . If Lyme carditis is suspected and there is evidence of conduction block — particularly severe atrioventricular block — hospitalisation for cardiac monitoring and empiric therapy is required while awaiting serology .
Serological studies require a twotier approach as false-positive results often occur because of cross-reactivity with other spirochaetal and viral infections . 2 An enzyme immunoassay ( EIA ) serological screening test is recommended . If positive or indeterminate , a confirmatory immunoblot assay should be performed . The EIA is not sufficiently specific as a standalone confirmatory test , although the newest assay in development — C6 peptide EIA — has increased specificity . 19
There are several difficulties with Lyme disease serological assays that can lead to false-positive results , particularly in Australia , which has a low-prevalence population , reducing the positive predictive value . Initial first-generation serology tests were derived from cultured spirochaetes that do not express many of the immunogenic proteins that occur when in the vertebrate host . Second- and third-generation tests
CDC / James Gathany / bit . ly / 308r1Fw
Figure 3 . Erythema migrans .
Guswen / CC BY-SA 4.0 / bit . ly / 3Z8w5IA
Figure 4 . Erythema migrans .